The patent specifications of JP 4307510B (Patent Document 1) and JP 4451924B (Patent Document 2) disclose a method configured to: form two different types of polarizing film sheets, using a pair of polarizing film-containing laminate webs having respective widths corresponding to long and short sides of a liquid crystal display panel having a rectangular shape; and successively laminate the polarizing film sheets, respectively, on opposite surfaces of the liquid crystal display panel, in such a manner as to allow transmission axes of the polarizing sheets to orthogonally intersect each other, to produce a liquid crystal display device.
Further, each of JP 2009-271516A (Patent Document 3) and JP 2012-128409A (Patent Document 4) discloses a method and an apparatus configured to: sequentially unroll at least a pair of laminate webs; cut out at least two different types of film sheets, respectively, from the laminate webs; and sequentially superimposingly laminate the film sheets to one surface of a liquid crystal display panel having a rectangular shape, to form a laminate. In particular, the Patent Document 4 discloses a process comprising: attaching, to one surface of a liquid crystal display panel which is being conveyed in a posture where a short side of the liquid crystal display panel is oriented to serve as a leading edge thereof, a first film sheet formed from a laminate web having a width corresponding to the short side, in such a manner as to have a length corresponding to a long side of the liquid crystal display panel; and then superimposingly laminating, to an outer surface of the first film sheet on the liquid crystal display panel which is being conveyed in a posture where the long side of the liquid crystal display panel is oriented to serve as the leading edge, a second film sheet formed from a laminate web having a width corresponding to the long side, in such a manner as to have a length corresponding to the short side.
The Patent Document 3 proposes a retardation film to be laminated to a polarizing film, and describes a technique of laminating two or more types of retardation film sheets to control retardation-dependent optical properties or the like. A ¼ wavelength plate, a circularly polarizing plate and a display device produced in the above manner are disclosed in JP 2002-311239A (Patent Document 5).
As is clear from the above Patent Documents, generally, a substrate composing, but not limited to, an optical display device such as a liquid crystal display device incorporating a reflective polarizing film sheet is continuously produced by the following process. A reflective polarizing film is different from a normal absorptive polarizing film, in terms of structure and function. Specifically, in terms of a relationship between a direction of a transmission axis and a stretching direction, the reflective polarizing film is different from a normal absorptive polarizing film uniaxially stretched in a longitudinal direction thereof, by 90 degrees. Therefore, in a process for producing a liquid crystal display device incorporating a reflective polarizing film sheet, it is necessary to superimposingly laminate two different types of film sheets to form a laminate, on a non-viewing side of a liquid crystal display panel, in such a manner that respective transmission axes of an absorptive polarizing film sheet and the reflective polarizing film sheet become parallel to each other.
As above, in the process for producing such a liquid crystal display device, there is an unsolved technical problem in the steps of: continuously unrolling an absorptive polarizing film-containing laminate web and a reflective polarizing film-containing laminate web; cutting out an absorptive polarizing film sheet from the absorptive polarizing film-containing laminate web and attaching the absorptive polarizing film sheet to a non-viewing side of a liquid crystal display panel being conveyed; and then cutting out a reflective polarizing film sheet from the reflective polarizing film-containing laminate web, and, after turning the liquid crystal display panel by 90 degrees, superimposingly laminating the reflective polarizing film sheet to an outer surface of the absorptive polarizing film sheet on the liquid crystal display panel. There is the same technical problem in a process for producing an organic EL display device, which comprises the steps of: sequentially cutting out a circularly polarizing film sheet and a retardation film sheet, respectively, from a circularly polarizing film-containing laminate web and a retardation film-containing laminate web; and superimposingly laminating the retardation film sheet to an outer surface of the circularly polarizing film sheet to be attached to a viewing side of an organic EL display panel being conveyed.
The technical problem is that, in a process for producing two rolls of laminate webs to be used in pair, although there is a need for cutting each of the rolls to a width corresponding to a long or short side of a rectangular panel onto which a laminate is to be formed, it is actually difficult to accurately cut each of the rolls to a desired roll width, and thereby it is necessary to employ the step of cutting out film sheets using such rolls each of which is non-uniform in terms of roll width, and superimposingly laminating the film sheets together. There are two problem caused by the non-uniformity in roll width.
One of the problems is to meet a need for realizing a narrower frame in a display device by reducing a width of a non-display region formed along four sides of a display panel. In recent years, along with progress in polarization toward a larger size and a smaller size of a liquid crystal display, there is an increasing need for realizing a narrower frame in a large-size display and obviously there is also an increasing need for realizing a narrower frame in a tablet liquid crystal or organic EL display device which is subjected to further downsizing. Specifically, in the case where a laminate of two different optical film sheets is formed on a display panel, there occurs a situation where a short side of an optical film sheet cut out from one of a pair of laminate webs each of which is non-uniform in terms of width is not coincident with a short side of an optical film sheet cut out from the other laminate web in such a manner as to have a length corresponding to a short side of the display panel. It is not always easy to solve this problem by enhancing cutting accuracy in production of rolls. Therefore, it is necessary to realize a narrower frame of a display screen in a display device by making short sides or long sides of two different film sheets coincident with each other, on the assumption that each of two rolls to be used in pair becomes non-uniform in terms of roll width.
The other problem is that, in the case where a laminate is formed on one surface of a display panel by using two different first and second film sheets cut out, respectively, from laminate webs fed from two rolls which are used in pair and each of which is non-uniform in terms of roll width, if a size of the second film sheet superimposed on the first film sheet is greater than that of the first film sheet, and a pressure-sensitive adhesive layer of the second film sheet lies outside the first film sheet, a resulting display device becomes defective. This is a problem insoluble by a lamination accuracy inspection method disclosed, for example, in JP 2011-197281A (Patent Document 6) and JP 5022507B (Patent Document 7). Therefore, there has also been proposed an idea of forming the second film sheet to have a size less than that of the first film sheet. However, this solution must be inconsistent with fulfillment of the need for realizing a narrower frame.